If like literally produced like, without any variation, there would be neither dog shows nor field trials. Nor would there be any dog breeders, though, of course, some people might raise dogs to supply a demand for a useful animal just as manufacturers turn out tenpenny nails, sugar coated pills, and lead pencils.

Variation is the raison d'être of the bench show and the field trial. Just imagine a judge confronted by a class of Boston Terriers in which every single entry was absolutely identical in conformation, size, markings, and disposition. It would be like trying to select the best of a paper of pins. Try for a moment to wax enthusiastic over a field trial in which every bird dog not only looked just alike, but was blessed with the same nose, speed, bird sense, and training. It would be about as thrilling as a coursing match on treadmills.

Moreover, variation is the backbone of breeding. Contrast the mingled hopes and fears of the breeder who studies for the first time the puppies of a new-born litter with what his feelings would be were he absolutely certain that every last youngster in the lot was an exact reproduction of its sire and dam. For a time, to be sure, there would be some interest in crossing established varieties. Even this would be quite mechanical, and the results could be foretold with discouraging accuracy. Moreover, our many times great grandfathers would long, long ago have exhausted the possibilities of such cross-breeding, which, if persisted in under a condition of heredity without variation, would eventually result in the development of a single breed, the great average dog, the exact mean of all varieties. He might be a very remarkable dog to look at, but he would hardly prove an interesting animal in the breeding kennels.

It is due to variation that the breeder is enabled to make a choice. Only when a choice is presented is there any possibility of improvement. It is very obvious that variation is an important subject for the dog breeder. There are a number of very practical problems that are brought much closer to their correct solution by a better understanding of variation.

What breeder, for example, would not like to know the exact limits of variation, and how much it can be controlled? Whether or not variations are correlated, and does a long head of necessity mean a long back? What kinds of variations are most surely inherited; which are hardest to fix in a strain; which are easiest to lose? These questions, and others like them, can be applied by any breeder to his own dogs. It is easy to appreciate their vital importance. A clearer understanding of the nature of variations of all kinds is certain to be a very practical help.

Dog fanciers are fairly brought up on variation: their shows and trials are based upon it, and their breeding would be aimless without it. They have trained their eye to appreciate slight differences in dogs that an ordinary person never notices; but, skilled as our judges and breeders are in recognizing the slightest gradations, they are not in the habit of distinguishing between different kinds of variations and of classifying them. These distinctions are important. Their recognition avoids considerable confusion. They are, moreover, rather obvious once the attention is directed to them.

In the first place, there are variations of form and variations of function. The bench show enthusiast is deeply concerned with the former. A Collie breeder, for example, is very anxious to perfect a long, clean skull with a level mouth and filled in foreface, topped off with semi-prick ears (all matters of structure). The follower of the field trials, on the other hand, lays most emphasis on functional variations. A Pointer man is vitally interested in his dog's speed, nose, and endurance (all matters of function). Oft and again the bench show fancier has been charged with utter indifference to vitality, disposition, and intelligence. The unconcern of the field dog owner to the looks of his animals is proverbial. Evidently, both display a lop-sided interest in their dogs, but this is really not so serious as some alarmists would have us believe.

The breeder whose sole object is to produce dogs that will win championship points and silverware knows full well that shyness and viciousness, constitutional weakness, and the tendency to develop certain diseases are all to be religiously avoided. The keenest field trial follower appreciates that speed and endurance are dependent upon good conformation. All breeders are concerned with the functional variations of fertility and impotence, of exceptional prepotency as a breeding individual, of the tendency to abortion or to faulty milk supply displayed by some bitches. On the other hand, no breeder wants to breed unsound, cripples.

Again, all variations can be classed as either quantitative or qualitative. They are all either differences in degree or differences in kind. Of two Toy Spaniels one may grow a very full, profuse coat; the other may always be comparatively short haired. This is a quantitative variation, a degree of difference. The texture of one coat may be fine and silky, without the slightest tendency to curl, and the other coat may be coarse and decidedly wavy. This is a qualitative variation, a difference in kind. All variations in size and shape are quantitative. Variations in substance and material, as texture, coloring, dispositions, etc., are qualitative. It is usually considered that the qualitative variations are easiest to fix and also easiest to lose. It is therefore useful for a breeder to learn to make the distinction between the two and to keep this distinction before him in his breeding operations.

Still a third classification can be made of variations. They are either continuous or discontinuous. The great majority of all variations with which the breeder is concerned are continuous. In fact, it is hard, with the exception of color and markings, to fix on any variations of importance to the dog breeder that are strictly discontinuous. The two different kinds are easily distinguished. A recently proposed English Standard for the Fox Terrier gives the ideal length of head as seven inches measured from the nose to the occiput with calipers. If all Fox Terrier heads in the world were so measured, we should find some longer and many shorter than this ideal. There would, however, be a continuous series of lengths without any sharp breaks. Every possible length from eight to five inches (assuming that these are the limits) would be represented. The length of head is a continuous variation, but the coloring of the head is a discontinuous variation. We should find many were black, white, and tan; some black and white, and also tan and white; fewer would be all black, or all white, or all tan. There would, however, be no intermediate shades of greys, blues, brindles, smuts, or fawns. These colors are not found in pure bred Fox Terriers. They could only be obtained by resorting to cross-breeding.

A moment's reflection will convince any experienced fancier that continuous variation is the one that almost exclusively enters into his breeding operations. It is probable, however, that some of the fancy points of our highly artificial breeds have originally arisen from discontinuous variations. It seems probable, in lack of any direct proof, that the screw tail of the English Bulldog, for example, first appeared as a mutation, or a sudden discontinuous variation. There is plenty of evidence contributed by the Dutch botanist De Vries to prove that these mutations are continually appearing in various forms of plant and animal life, and that they breed true without reverting to the ancestral form. It is certainly feasible to suppose that the screw tail first appeared as a mutation. Of course, it has been carefully preserved and improved by selection, and even been bred into other varieties, the Boston Terrier and the French Bulldog.

It lies within the range of possibility to breed a Fox Terrier head a hair's breadth longer and another a hair's breadth shorter than seven inches. Obviously in the case of discontinuous variations the opposite is true, and no amount of selection, without any cross-breeding, would produce a gray marked Fox Terrier.

It has been boastfully said that, if they would, breeders could produce a dog without a head—the Old English Sheepdog and the Schipperke are living proofs of the ability to produce a dog without a tail—but there are certain very definite limits to what can be accomplished by means of artificial selection. This is particularly true in the case of discontinuous variations. To remember this, and to differentiate between the continuous and discontinuous, may prevent a foolish waste in striving after the unattainable.

We have already seen how bisexual reproduction and the reduction of the male sperm and the female ovum introduce a primary cause for variation. There are other internal causes of variation.

Dog fanciers are generally credited with a pretty firm belief in telegony. Certainly it is not unusual to hear the opinion expressed that, if a bitch is mismated with a mongrel or a dog of a different breed from her own, she is spoiled for breeding purposes. It is supposed that the mesalliance will affect the character of her subsequent puppies. During the past ten years there has been a continually increasing number of fanciers who place no credence in the belief that a previous sire affects subsequent litters. The belief, however, lingers, chiefly among "novices" and "old-timers," and every once in a while we hear of a case supposed to prove the contention.

The late F. H. McConnell personally related to me an experience of his, which I offer for what it may be worth. A wire Fox Terrier bitch of his was mismated to an Irish Terrier dog. The resulting puppies were such demons on rats that the experiment was intentionally repeated, but the third time she was bred to a thoroughbred Fox Terrier, a dog, if I remember correctly, of the Warren strain. The pups of this litter were said to show very unmistakable signs of Irish Terrier characteristics.

Be that as it may, the weight of all scientific evidence is against a belief in telegony. The recorded examples are few and far between, and direct experiment has never yielded anything but negative results. Darwin cited the famous case of Lord Morton's thoroughbred mare. She had a hybrid colt sired by a quagga. Afterwards she foaled twice to a thoroughbred stallion, and both of these colts were marked with bars over the shoulders and on the legs, supposed effects of the quagga upon the get of the stallion. However, Professor Ewart of Edinburgh repeatedly performed the same experiment on a large scale and was unable to find any traces of the quagga in any but the direct hybrids of the cross-breeding.

To discard a good bitch because she has thrown puppies to a strange dog seems, in the light of all evidence, to be a bit fanatical. She should certainly be given the benefit of the doubt, and probably most fanciers would be inclined to at least give her a trial. Professor Davenport of the University of Illinois made a canvass among dog fanciers to find out how many believed in the effect of previous matings. He received thirty-seven replies—one from a believer in telegony; two, non-committal; six, uncertain; and twenty-eight denials. These figures, and from my own experience I consider them indicative of the facts, show that the great majority of dog breeders are not believers in telegony.

Another supposed cause of variation is the impression upon the embryo of certain sights, sounds, colors, etc., that affect the dam while carrying the offspring. This very old belief is more widespread among horse and cattle breeders than among dog fanciers. In the Bible we read that Jacob, to increase the number of spotted offspring which were to be given to him, set up peeled sticks before the herd. It is, however, generally considered that instances of pre-natal influence through external sources are to be regarded more in the nature of strange coincidences than of any serious cause for variation.

Horse and cattle breeders, however, have gone to rather fantastic extremes in this belief, hanging up colored blankets or holding desirably colored animals in front of females during service. I have heard a few similar cases in dog breeding. The English Bulldog Tidal Bishop, white with brindle markings and bred from white pied stock, invariably got dark brindle puppies, thanks, it was rumored, to the foresight of his owner in holding a brindle dog in front of the bitches he served. Practical breeders, however, disregard these pre-natal influences entirely, or at best regard them with skeptical curiosity.

Reversion to ancestors back of the immediate parents has been often observed in kennels, and it certainly presents a form of variation. It, however, belongs more to the study of heredity. We shall see later that it is capable of a reasonable explanation.

The various external forces and their effect upon variation have long been a subject for debate. The trend of biological evidence is more and more against a belief in inheritance of modifications due to environment. Of course, every breeder appreciates that puppies bred from stock that is carefully fed, properly housed, and well exercised will be healthier and stronger than those whelped in kennels where the conditions of life are less ideal. This, however, is more a matter of development than of variation.

It has been frequently observed that the number of puppies in a litter is larger among domesticated dogs than among the wild canidae. Abundant food and protection from the extremes of weather have doubtless been the main factors in this increase.

The instances of deterioration in British breeds of dogs introduced into India have been often quoted from Darwin, but since he collected his information additional facts have been brought forward. A strong dog fancy has developed in India, with numerous shows under the jurisdiction of the Indian Kennel Club. Judging from descriptions and photographs, Indian breeders have been able to produce dogs that compare favorably with their direct importations from England, and to-day we hear little about the degeneration of dogs in the eastern country. Moreover, the success of the Airedale Terrier in the Philippines and throughout tropical America is further confirmation of the fact that climate does not have such a direct bearing on variation as was formerly supposed.

In America we sometimes hear complaints that the extremes of temperature and the dryness of the air (compared with the climate of Great Britain) ruin the correct texture of a wire coat. Many terrier owners have never been able to find any direct confirmation of this belief. It is certain that dogs brought to a new country have to become acclimated just as people do, but there is only the scantiest evidence that this has any direct bearing upon their offspring with which a practical breeder must reckon.

Many of the external forces affecting dogs are closely allied in their nature to acquired characteristics. These will be discussed later. Some consideration of them, however, belongs to the subject of variation. The best working rule, in view of the disputed importance of these external forces, will be to take no chances. Kennels should be so arranged and so managed as to keep the breeding stock in the very best possible condition, so affording the most favorable opportunity for the action of these external forces in the desired direction.

Fig. 5.—Showing the actual variation in
height of 8,585 British men.

We have now classified the different types of variation and considered briefly the principal causes at work to produce them. We have seen that every variation is either structural or functional; quantitative or qualitative; continuous or discontinuous. We have taken up the causes of variation in bisexual reproduction; in reduction of the germ cells, in telegony, in pre-natal impressions; in reversion, and in various external forces. Having in our minds a clearer idea of the nature of variation, let us see how variation behaves.

By the very definition of continuous variation we expect—and rightly so—to be able to get all possible shades of differences. These differences can be expressed more accurately and clearly by a graph than in any other way. The accompanying figure (Fig. 5), which is taken from J. A. S. Watson's little handbook "Heredity," expresses graphically the variation in the height of 8585 British men.

The vertical lines represent the differences in height in inches and the horizontal lines show the number of men in hundreds. The very top of the curve is at a point between 67 and 68 inches and a little over the line of 1300 individuals. This means that of the 8585 men measured there were over 1300 who were roughly 67½ inches tall. There were 1200 men who were something over 66 inches tall, and also 1200 men who were 69 inches tall. The curve expresses graphically the average height and the variation from that average of the men measured. It is merely another way of saying "Most men are an average height"; but it also shows that that average is close to 67½ inches.

Another thing that this curve shows us is that the deviation from the average is quite uniform. There are just about as many men taller than the average as there are men shorter than the average. Not only this, but just about as many men are two inches above as there are men two inches below the average height. The curve is remarkably regular on both sides of the apex.

A great amount of similar data has been carefully collected, measuring not only variations in men but also in plants and animals. The figures so collected have been graphically expressed in the same way. The curves thus derived have been found to be remarkably similar, all being very close to the normal variability curve, as it is called. This normal curve is shown in Fig. 6, and one can see at a glance how close to it is the curve of the height of the 8585 men. The differences in the height curve from the normal are accounted for by the number of men measured. Had eight million heights been recorded instead of eight thousand, the curve would more closely approach the normal.

All this has a very practical meaning for dog breeders. It proves to us that all continuous variations have a decided average and that the falling off in numbers, at first quite fast, very fast in the middle portion, and slower at the extremes, is remarkably even on both sides of the average. Applying this normal variability curve to the ideal length of a Fox Terrier's head, we should find, assuming that the average would be six inches, that just about as many had heads only five inches long as had the ideal length of seven inches. These figures are, of course, purely arbitrary. There is no data available on the length of Fox Terrier heads. It is, however, quite certain that, if the ideal is seven inches, the average would be below this. In real life "an inch on a terrier's head is a good deal," but the even figures were taken for simplicity's sake. The variation would not be so great, but this does not affect our example.

Most dog fanciers will be surprised to find that variation is such a regular and consistent thing. We are quite prone to regard all variations as sudden, freakish, and more or less unreasonable. It is only by studying great numbers that the regular and symmetrical continuity of all variation becomes apparent. Working with individuals, we get the erroneous idea that all variations are sudden and irregular. There are such variations, mutations, but these are not the variations with which dog breeders are commonly working.

Very gradual variations, both good and bad, are being continually presented to the dog breeder for his choice. The great difficulty lies in the fact that the dog is made up of such a great number of distinct points. Very seldom does a dog appear which combines any considerable number of variations all in the desired direction. We are, accordingly, forced to sacrifice one point for the advantage of another. In this the dog breeder has the opportunity for displaying his rarest judgment, and in making these choices he will be benefited by knowledge both of variations and of their inheritance.

If the sole and only object of the Fox Terrier breeder were to produce a dog with a head seven inches long, this could be accomplished in a comparatively short time. But besides that seven inch head he wants a well shaped head, nicely balanced, with a flat skull, clean cheeks, and well filled in foreface; a well placed and correctly shaped, dark eye; sound, level teeth, just covered with tight lips; small, V-shaped ears, placed on the corner of the skull and faUing forward—and we have not yet gone "behind the collar"! The neck, shoulders, front, ribs, back, loins, hindquarters, feet, tail, height, weight, bone, coat, and style, each one must be considered in as careful detail as mere length of head. Not only this, but the relative positions of each part and its proper combination with other points is vitally important.

It is small wonder that the perfect dog of any breed has yet to be bred. The ideal is tremendously improbable, but it is at least conceivably possible. No fancier has ever seen a perfect dog—excepting, of course, one of his own home-bred puppies who died very young!—but we have all seen dogs that in one or two, possibly even in half a dozen different points, were our ideal. That these few points have appeared in accordance with our ideals is a pledge of good faith on the part of variation to supply us with the required material out of which to make absolute perfection.

The variations, both good and bad, which are being continuously presented for our selection are, we have seen, always clustering round the average. Their causes are often mysterious, but we have much knowledge on which to base our breeding operations. We are able to get a clear idea of the nature of the various kinds of variations and to appreciate that they normally swing evenly on each side of the average. This knowledge will help the breeder when he comes to employ the advantageous variations, through the agency of heredity, in his efforts to breed the ideal dog.